In the prior art, a description has already been given of electrical power supply converters which, as a function of commands entered via an on-board computer or directly via switches on the instrument panel, place a halogen bulb in a particular operating condition.
However, since the first converters appeared, the electronic environment inside the vehicle has changed somewhat and thus a certain number of problems or requirements have arisen which the present invention aims to solve.
It was found that the service life of the halogen bulbs used in the headlamp and/or indicator lamp was on average much shorter than the service life indicated by halogen bulb manufacturers. This is because the operating voltage of the alternators used in vehicles has gradually increased.
Furthermore, some xenon bulbs in particular shared the same connection cables with the halogen bulbs, and these connection cables had to be of low electrical impedance in order to ensure correct electrical behavior.
This means that the voltage applied to the terminals of the halogen bulbs was often greater than the optimal voltage which makes it possible to ensure the reliability of halogen bulbs.
Moreover, the luminous flux of halogen bulbs closely depends on the voltage applied thereto. This means firstly that the luminous flux becomes too great on account of the increase in the source voltage, in particular in indicating devices such as a flashing light or a day running time indicator lamp, and on the other hand that irregularities in the luminous flux occur on account of the mismatched impedance due to the cables, and this is prejudicial both to the lighting and/or indicating comfort and also to the increase in the number of disadvantages due to parasitic radiofrequency radiation (EMC).
A number of solutions are proposed in the prior art.
According to a first solution, use is made of a cable for connecting the converter to the bulb, which cable has high impedance in order to cause a voltage drop due to losses. This results in a reduction in the 10 voltage applied to the halogen bulb, and this is beneficial to the service life thereof. Nevertheless, a connection cable with high impedance is expensive and must be avoided in mass production.
According to a second solution, use is made of a halogen bulb which has a longer nominal service life than the nominal service life of the bulbs used to date. Such a measure is essentially achieved by using batches of halogen bulbs in respect of which the constraints which provide a longer service life have been increased. This involves a significant extra cost and must be avoided in mass production.
According to a third solution, use is made of a power supply converter for supplying power to each halogen bulb based on the principle of a switch-mode power supply in respect of which the output voltage can be regulated independently of the supply voltage. However, such a solution introduces a switch in the current which flows on the power supply cable which connects the output of the converter to the bulb, and this results in electromagnetic interference which increases the risk of not meeting EMC standards in motor vehicles.
Finally, all of these solutions have the drawback of producing a mediocre yield on account of electrical losses in particular on the power supply cables. Moreover, the dispersion of the impedances of the connection cables and the difference in their lengths, depending on the relative situation of the control unit and of each headlamp or light, entail the risk that the voltage applied to the right headlamp or light will be different from the voltage applied to the left headlamp or light.